1. Field of the Invention
The present invention relates to a liquid housing container that houses a liquid such as ink and a liquid supply apparatus.
2. Description of the Related Art
As a container that houses a liquid, a liquid housing container is conventionally known which has a gas-liquid separation membrane that passes a gas, while controlling the passage of a liquid. For example, Japanese Patent Application Laid-Open No. 61-24458 proposes an ink jet print head having an ink tank in which a gas-liquid separation membrane is installed. An opening formed in a part of the ink tank is covered with the gas-liquid separation membrane. The gas-liquid separation serves to remove bubbles from the ink tank, while preventing the leakage of ink.
By installing a membrane having such a gas-liquid separating capability in the opening in the liquid housing container, it is possible to house the liquid without leakage and to remove the gas from the liquid housing container through the membrane.
However, liquid housing containers using the conventional gas-liquid separation membrane are not sufficiently durable. For example, if an ink tank is used over a long period in which the conventional gas-liquid separation membrane is installed as disclosed in Japanese Patent Application Laid-Open No. 61-24458, ink (liquid) may soak into the gas-liquid separation membrane to reduce the air permeability of the gas-liquid separation membrane. Further, the gas-liquid separation membrane may fail to block the ink, which may leak to the outside of the ink tank. This may result in contamination or malfunction of the printing apparatus.
Such defects tend to be more marked when the surface tension of the liquid is lower. However, a lower surface tension has increasingly been requested for ink for ink jet printing apparatuses, for example.
Specifically, a problem may occur when an operation is repeated which involves making a difference in atmospheric pressure between the interior and exterior of the liquid housing container to remove the gas from the container to the exterior through the gas-liquid separation membrane. In this case, the liquid blocking capability of the gas-liquid separation membrane may be prematurely degraded. The liquid may then soak into the gas-liquid separation membrane, resulting in the leakage of the liquid. In particular, with such an ink tank as disclosed in Japanese Patent Laid-Open No. 61-24458, an operation of removing the internal gas through the gas-liquid separation membrane must often be repeated a number of times. It is thus important to ensure the repeated durability of the gas-liquid separation membrane.
Further, the gas-liquid separation membrane used for such an ink tank needs to have as high an air permeability (the amount of gas permeated per unit area) as possible in order to reduce the pressure difference or time required to remove the gas from the ink tank. Moreover, a high positive pressure may be temporarily exerted on the ink by the expansion of the ink caused by a change in temperature or the vibration or turn-over of the ink tank during transportation. Accordingly, to reduce the possibility that the ink leaks to the exterior through the gas-liquid separation membrane, the gas-liquid separation membrane must have a high withstanding hydraulic pressure. The withstanding hydraulic pressure means a limiting pressure required to exert pressure on a liquid such as ink which is in tight contact with the gas-liquid separation membrane to pass the liquid through the gas-liquid separation membrane.